Field of the Invention
The invention relates to a steam turbine with an interior through which an action steam can flow and with a condenser for condensing the action steam. The invention further relates to a method of cooling a steam turbine, in particular a low-pressure steam turbine, in the ventilation mode.
U.S. Pat. No. 1,447,081 describes a reaction steam turbine without a condenser. In that steam turbine, a flow connection is made via a by-pass conduit between a conduit subjected to a steam flow and a region between an idly running high-pressure and low-pressure part. A valve must be opened in order to make the connection. The turbine is, in particular, a marine turbine plant which is configured for forward (ahead) operation and reverse (astern) operation.
For forward operation, the turbine has a blade section comprising a impulse section, a high-pressure reaction section and a low-pressure reaction section. For reverse operation, the turbine has a further additional impulse section which is located axially downstream of the low-pressure reaction section and which acts on the same turbine shaft. A steam flow emerging from the low-pressure reaction section during forward operation is discharged into the same exhaust-steam connection piece as a steam flow through the impulse section for reverse operation. The low-pressure reaction section and the impulse section for reverse operation are consequently in fluidic communication with one another. In reverse operation, therefore, at least a small portion of steam passes into the low-pressure reaction-section. In order, in this case, to prevent the steam from standing, which, due to the rotation of the idly running low-pressure blades, would lead to heating of the blades, a bypass conduit leading from a chamber between the high-pressure and the low-pressure section to the exhaust-steam connection piece is provided. The valve which must be closed during the forward operation of the turbine is disposed in the bypass conduit.
It has become known, for example from the disclosure in European patent EP 0 602 040 B1, to cool a low-pressure steam turbine in the ventilation mode, the rotor of the steam turbine being rotated without being subjected to expanding steam. Such a ventilation mode occurs, for example, in a multi-cylinder turbo set, in which there is provided, upstream of a low-pressure steam turbine, a possibility of diverting action steam, otherwise to be expanded in the low-pressure steam turbine, into a heating heat exchanger or the like. Cooling in the ventilation mode is carried out, according to EP 0 602 040 B1, by feeding steam into a tapping point provided between an inlet for the action steam to be expanded and an outlet for this steam. The tapping point is connected, for example, to the steam space of a condenser, the quantity of steam supplied and/or of condensate supplied being regulated as a function of a temperature value determined in the steam turbine. As compared with injection at the outlet, during which the cooling effect is restricted to parts of the turbine in the vicinity of the outlet, the advantage of feeding steam into a tapping point is that turbine components located further upstream are also cooled. Injection at the inlet of the steam turbine may possibly lead to condensate agglomerating in the region of the inlet and putting the blading of the turbine at risk from surging. This is likewise avoided by feeding steam into a tapping point.
Cooling of the turbine in the ventilation mode is advantageous, in particular, because, in the ventilation mode, there is in the turbine a steam atmosphere, the static pressure of which corresponds to the pressure prevailing in the condenser connected to the low-pressure steam turbine. The friction of the turbine blades on this steam (ventilation) may lead to a considerable amount of heat being generated, with the result that the turbine may be heated to high temperature and, in the extreme case, thereby subjected to an inadmissible load.